ajax loader and file download problem

hi

i have linkbutton which creates Excel file and then download it. since creating file takes more than 5 seconds i'd like to use ajax loader (clock) to show user that creating file is in progress. so i used updatePanel to perform this, but if i use <triggers> download works and ajax loader doesn't.

 if i don't use <triggers> ajax loader works, but download doesn't

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <Triggers>
            <asp:PostBackTrigger ControlID="lbtnExportXlsControl" />
        </Triggers>
    <ContentTemplate>
    <div class="divlbtn1">
        <asp:LinkButton CssClass="lnkbtn" ID="lbtnExportXlsKontrolni" runat="server">Export (Excel kontrolni)</asp:LinkButton>
    </div>
</ContentTemplate>
    </asp:UpdatePanel>

<asp:UpdateProgress ID="UpdateProgress2" AssociatedUpdatePanelID="UpdatePanel1" runat="server">
        <ProgressTemplate>
            <img alt="Creating Excel ..." src="images/AjaxLoader_blue_clock_24.gif" />
            Creating Excel ...
        </ProgressTemplate>
    </asp:UpdateProgress>

so, how to handle this both to work?